A conventional potentiostat uses an electrochemical cell with two or three electrodes, e.g., a reference electrode, a counter electrode, and a working electrode. The potentiostat is an electronic instrument that controls a voltage difference between a working electrode and a reference electrode. These electrodes are contained in an electrochemical cell. The potentiostat implements this control by injecting current into the cell through a counter electrode. In most applications, the potentiostat measures the current flow between the working electrode and the counter electrode.
The working electrode is the electrode where the potential is controlled and where the current is measured. Thus, the working electrode serves as a surface on which the electrochemical reaction takes place. The reference electrode is used to measure the working electrode potential and should have a constant electrochemical potential as long as no current flows through it. Lastly, the counter electrode is a conductor that completes the cell circuit and is generally an inert conductor. A current flowing into the solution via the working electrode leaves the solution via the counter electrode.